A new state law now in effect leaves no doubt anymore…you cannot be held civilly liable for breaking into a vehicle in an effort to save an infant or a small child left unsupervised. Sergeant Scott White, with the Missouri Highway Patrol says, however, there are two things you must first do under the circumstances before smashing out a window.
Sergeant White also says, if you are going to break out a car window to save a child, go to a window as far away from the child as possible. There is a tool available in most hardware stores specifically designed to break out a car window in the case of an emergency. Otherwise, a large rock or a brick will usually do the job as well.